1. Field of the Invention
The present invention relates to a zoom lens, more particularly to a cam mechanism, incorporated in the zoom lens, for moving optical elements such as lens groups.
2. Description of the Related Art
In conventional zoom lenses, it is often the case that a cam ring incorporated therein is provided on an inner peripheral surface or an outer peripheral surface thereof with a set of cam grooves for moving a linearly guided optical element such as a lens group. Each of these cam grooves is usually provided, at the opposite ends of a photographing section (zooming section) thereof between a wide-angle extremity position and a telephoto-extremity position, with an adjustment marginal section which allows the associated cam follower to move beyond a predetermined position thereof at the wide-angle extremity of the zoom lens (hereinafter referred to as a wide-angle marginal section) and another adjustment marginal section which allows the associated cam follower to move beyond a predetermined position thereof at the telephoto extremity of the zoom lens (hereinafter referred to as a telephoto marginal section), respectively.
However, such a cam groove design makes it impossible for two optical elements (e.g., two lens elements), adjacent to each other in the optical axis direction of the zoom lens, to be brought close to each other until the closest limit at the wide-angle extremity or the telephoto extremity of the zoom lens, because the moving amounts of the two optical elements for the wide-angle marginal section and the telephoto marginal section, respectively, must be taken into account if each cam groove is provided at the opposite ends thereof with the wide-angle marginal section and the telephoto marginal section, respectively. This has been a bottle neck in miniaturizing the zoom lens and in increasing the zoom ratio of the zoom lens system.